/* 
 * Copyright (C) 2013 The Rythm Engine project
 * Gelin Luo <greenlaw110(at)gmail.com>
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
*/
package org.rythmengine.utils;

import java.io.Serializable;
import java.text.ParseException;
import java.util.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Time utils
 */
// Some of the code come from Play!Framework Time.java, under Apache License 2.0
public class Time {

    static Pattern days = Pattern.compile("^([0-9]+)d$");
    static Pattern hours = Pattern.compile("^([0-9]+)h$");
    static Pattern minutes = Pattern.compile("^([0-9]+)mi?n$");
    static Pattern seconds = Pattern.compile("^([0-9]+)s$");

    /**
     * Parse a duration
     *
     * @param duration 3h, 2mn, 7s
     * @return The number of seconds
     */
    public static int parseDuration(String duration) {
        if (duration == null) {
            return 60 * 60 * 24 * 30;
        }
        Integer toAdd = null;
        if (days.matcher(duration).matches()) {
            Matcher matcher = days.matcher(duration);
            matcher.matches();
            toAdd = Integer.parseInt(matcher.group(1)) * (60 * 60) * 24;
        } else if (hours.matcher(duration).matches()) {
            Matcher matcher = hours.matcher(duration);
            matcher.matches();
            toAdd = Integer.parseInt(matcher.group(1)) * (60 * 60);
        } else if (minutes.matcher(duration).matches()) {
            Matcher matcher = minutes.matcher(duration);
            matcher.matches();
            toAdd = Integer.parseInt(matcher.group(1)) * (60);
        } else if (seconds.matcher(duration).matches()) {
            Matcher matcher = seconds.matcher(duration);
            matcher.matches();
            toAdd = Integer.parseInt(matcher.group(1));
        } else if ("forever".equals(duration)) {
            toAdd = -1;
        }
        if (toAdd == null) {
            throw new IllegalArgumentException("Invalid duration pattern : " + duration);
        }
        return toAdd;
    }

    /**
     * Parse a CRON expression
     *
     * @param cron The CRON String
     * @return The next Date that satisfy the expression
     */
    public static Date parseCRONExpression(String cron) {
        try {
            return new CronExpression(cron).getNextValidTimeAfter(new Date());
        } catch (Exception e) {
            throw new IllegalArgumentException("Invalid CRON pattern : " + cron, e);
        }
    }

    /**
     * Compute the number of milliseconds between the next valid date and the one after
     *
     * @param cron The CRON String
     * @return the number of milliseconds between the next valid date and the one after,
     *         with an invalid interval between
     */
    public static long cronInterval(String cron) {
        return cronInterval(cron, new Date());
    }

    /**
     * Compute the number of milliseconds between the next valid date and the one after
     *
     * @param cron The CRON String
     * @param date The date to start search
     * @return the number of milliseconds between the next valid date and the one after,
     *         with an invalid interval between
     */
    public static long cronInterval(String cron, Date date) {
        try {
            return new CronExpression(cron).getNextInterval(date);
        } catch (Exception e) {
            throw new IllegalArgumentException("Invalid CRON pattern : " + cron, e);
        }
    }

    /**
     * Thanks to Quartz project, https://quartz.dev.java.net
     * <p/>
     * Provides a parser and evaluator for unix-like cron expressions. Cron
     * expressions provide the ability to specify complex time combinations such as
     * &quot;At 8:00am every Monday through Friday&quot; or &quot;At 1:30am every
     * last Friday of the month&quot;.
     * <P>
     * Cron expressions are comprised of 6 required fields and one optional field
     * separated by white space. The fields respectively are described as follows:
     * <p/>
     * <table cellspacing="8">
     * <tr>
     * <th align="left">Field Name</th>
     * <th align="left">&nbsp;</th>
     * <th align="left">Allowed Values</th>
     * <th align="left">&nbsp;</th>
     * <th align="left">Allowed Special Characters</th>
     * </tr>
     * <tr>
     * <td align="left"><code>Seconds</code></td>
     * <td align="left">&nbsp;</th>
     * <td align="left"><code>0-59</code></td>
     * <td align="left">&nbsp;</th>
     * <td align="left"><code>, - * /</code></td>
     * </tr>
     * <tr>
     * <td align="left"><code>Minutes</code></td>
     * <td align="left">&nbsp;</th>
     * <td align="left"><code>0-59</code></td>
     * <td align="left">&nbsp;</th>
     * <td align="left"><code>, - * /</code></td>
     * </tr>
     * <tr>
     * <td align="left"><code>Hours</code></td>
     * <td align="left">&nbsp;</th>
     * <td align="left"><code>0-23</code></td>
     * <td align="left">&nbsp;</th>
     * <td align="left"><code>, - * /</code></td>
     * </tr>
     * <tr>
     * <td align="left"><code>Day-of-month</code></td>
     * <td align="left">&nbsp;</th>
     * <td align="left"><code>1-31</code></td>
     * <td align="left">&nbsp;</th>
     * <td align="left"><code>, - * ? / L W</code></td>
     * </tr>
     * <tr>
     * <td align="left"><code>Month</code></td>
     * <td align="left">&nbsp;</th>
     * <td align="left"><code>1-12 or JAN-DEC</code></td>
     * <td align="left">&nbsp;</th>
     * <td align="left"><code>, - * /</code></td>
     * </tr>
     * <tr>
     * <td align="left"><code>Day-of-Week</code></td>
     * <td align="left">&nbsp;</th>
     * <td align="left"><code>1-7 or SUN-SAT</code></td>
     * <td align="left">&nbsp;</th>
     * <td align="left"><code>, - * ? / L #</code></td>
     * </tr>
     * <tr>
     * <td align="left"><code>Year (Optional)</code></td>
     * <td align="left">&nbsp;</th>
     * <td align="left"><code>empty, 1970-2099</code></td>
     * <td align="left">&nbsp;</th>
     * <td align="left"><code>, - * /</code></td>
     * </tr>
     * </table>
     * <P>
     * The '*' character is used to specify all values. For example, &quot;*&quot;
     * in the minute field means &quot;every minute&quot;.
     * <P>
     * The '?' character is allowed for the day-of-month and day-of-week fields. It
     * is used to specify 'no specific value'. This is useful when you need to
     * specify something in one of the two fileds, but not the other.
     * <P>
     * The '-' character is used to specify ranges For example &quot;10-12&quot; in
     * the hour field means &quot;the hours 10, 11 and 12&quot;.
     * <P>
     * The ',' character is used to specify additional values. For example
     * &quot;MON,WED,FRI&quot; in the day-of-week field means &quot;the days Monday,
     * Wednesday, and Friday&quot;.
     * <P>
     * The '/' character is used to specify increments. For example &quot;0/15&quot;
     * in the seconds field means &quot;the seconds 0, 15, 30, and 45&quot;. And
     * &quot;5/15&quot; in the seconds field means &quot;the seconds 5, 20, 35, and
     * 50&quot;.  Specifying '*' before the  '/' is equivalent to specifying 0 is
     * the value to start with. Essentially, for each field in the expression, there
     * is a set of numbers that can be turned on or off. For seconds and minutes,
     * the numbers range from 0 to 59. For hours 0 to 23, for days of the month 0 to
     * 31, and for months 1 to 12. The &quot;/&quot; character simply helps you turn
     * on every &quot;nth&quot; value in the given set. Thus &quot;7/6&quot; in the
     * month field only turns on month &quot;7&quot;, it does NOT mean every 6th
     * month, please note that subtlety.
     * <P>
     * The 'L' character is allowed for the day-of-month and day-of-week fields.
     * This character is short-hand for &quot;last&quot;, but it has different
     * meaning in each of the two fields. For example, the value &quot;L&quot; in
     * the day-of-month field means &quot;the last day of the month&quot; - day 31
     * for January, day 28 for February on non-leap years. If used in the
     * day-of-week field by itself, it simply means &quot;7&quot; or
     * &quot;SAT&quot;. But if used in the day-of-week field after another value, it
     * means &quot;the last xxx day of the month&quot; - for example &quot;6L&quot;
     * means &quot;the last friday of the month&quot;. When using the 'L' option, it
     * is important not to specify lists, or ranges of values, as you'll get
     * confusing results.
     * <P>
     * The 'W' character is allowed for the day-of-month field.  This character
     * is used to specify the weekday (Monday-Friday) nearest the given day.  As an
     * example, if you were to specify &quot;15W&quot; as the value for the
     * day-of-month field, the meaning is: &quot;the nearest weekday to the 15th of
     * the month&quot;. So if the 15th is a Saturday, the trigger will fire on
     * Friday the 14th. If the 15th is a Sunday, the trigger will fire on Monday the
     * 16th. If the 15th is a Tuesday, then it will fire on Tuesday the 15th.
     * However if you specify &quot;1W&quot; as the value for day-of-month, and the
     * 1st is a Saturday, the trigger will fire on Monday the 3rd, as it will not
     * 'jump' over the boundary of a month's days.  The 'W' character can only be
     * specified when the day-of-month is a single day, not a range or list of days.
     * <P>
     * The 'L' and 'W' characters can also be combined for the day-of-month
     * expression to yield 'LW', which translates to &quot;last weekday of the
     * month&quot;.
     * <P>
     * The '#' character is allowed for the day-of-week field. This character is
     * used to specify &quot;the nth&quot; xxx day of the month. For example, the
     * value of &quot;6#3&quot; in the day-of-week field means the third Friday of
     * the month (day 6 = Friday and &quot;#3&quot; = the 3rd one in the month).
     * Other examples: &quot;2#1&quot; = the first Monday of the month and
     * &quot;4#5&quot; = the fifth Wednesday of the month. Note that if you specify
     * &quot;#5&quot; and there is not 5 of the given day-of-week in the month, then
     * no firing will occur that month.
     * <P>
     * <!--The 'C' character is allowed for the day-of-month and day-of-week fields.
     * This character is short-hand for "calendar". This means values are
     * calculated against the associated calendar, if any. If no calendar is
     * associated, then it is equivalent to having an all-inclusive calendar. A
     * value of "5C" in the day-of-month field means "the first day included by the
     * calendar on or after the 5th". A value of "1C" in the day-of-week field
     * means "the first day included by the calendar on or after sunday".-->
     * <P>
     * The legal characters and the names of months and days of the week are not
     * case sensitive.
     * <p/>
     * <p>
     * <b>NOTES:</b>
     * <ul>
     * <li>Support for specifying both a day-of-week and a day-of-month value is
     * not complete (you'll need to use the '?' character in on of these fields).
     * </li>
     * </ul>
     * </p>
     *
     * @author Sharada Jambula, James House
     * @author Contributions from Mads Henderson
     * @author Refactoring from CronTrigger to CronExpression by Aaron Craven
     */
    public static final class CronExpression implements Serializable, Cloneable {

        private static final long serialVersionUID = 12423409423L;
        protected static final int SECOND = 0;
        protected static final int MINUTE = 1;
        protected static final int HOUR = 2;
        protected static final int DAY_OF_MONTH = 3;
        protected static final int MONTH = 4;
        protected static final int DAY_OF_WEEK = 5;
        protected static final int YEAR = 6;
        protected static final int ALL_SPEC_INT = 99; // '*'
        protected static final int NO_SPEC_INT = 98; // '?'
        protected static final Integer ALL_SPEC = new Integer(ALL_SPEC_INT);
        protected static final Integer NO_SPEC = new Integer(NO_SPEC_INT);
        protected static Map<String, Integer> monthMap = new HashMap<String, Integer>(20);
        protected static Map<String, Integer> dayMap = new HashMap<String, Integer>(60);

        static {
            monthMap.put("JAN", new Integer(0));
            monthMap.put("FEB", new Integer(1));
            monthMap.put("MAR", new Integer(2));
            monthMap.put("APR", new Integer(3));
            monthMap.put("MAY", new Integer(4));
            monthMap.put("JUN", new Integer(5));
            monthMap.put("JUL", new Integer(6));
            monthMap.put("AUG", new Integer(7));
            monthMap.put("SEP", new Integer(8));
            monthMap.put("OCT", new Integer(9));
            monthMap.put("NOV", new Integer(10));
            monthMap.put("DEC", new Integer(11));

            dayMap.put("SUN", new Integer(1));
            dayMap.put("MON", new Integer(2));
            dayMap.put("TUE", new Integer(3));
            dayMap.put("WED", new Integer(4));
            dayMap.put("THU", new Integer(5));
            dayMap.put("FRI", new Integer(6));
            dayMap.put("SAT", new Integer(7));
        }

        private String cronExpression = null;
        private TimeZone timeZone = null;
        protected transient TreeSet<Integer> seconds;
        protected transient TreeSet<Integer> minutes;
        protected transient TreeSet<Integer> hours;
        protected transient TreeSet<Integer> daysOfMonth;
        protected transient TreeSet<Integer> months;
        protected transient TreeSet<Integer> daysOfWeek;
        protected transient TreeSet<Integer> years;
        protected transient boolean lastdayOfWeek = false;
        protected transient int nthdayOfWeek = 0;
        protected transient boolean lastdayOfMonth = false;
        protected transient boolean nearestWeekday = false;
        protected transient boolean expressionParsed = false;

        /**
         * Constructs a new <CODE>CronExpression</CODE> based on the specified
         * parameter.
         *
         * @param cronExpression String representation of the cron expression the
         *                       new object should represent
         * @throws java.text.ParseException if the string expression cannot be parsed into a valid
         *                                  <CODE>CronExpression</CODE>
         */
        public CronExpression(String cronExpression) throws ParseException {
            if (cronExpression == null) {
                throw new IllegalArgumentException("cronExpression cannot be null");
            }

            this.cronExpression = cronExpression;

            buildExpression(cronExpression.toUpperCase(Locale.US));
        }

        /**
         * Indicates whether the given date satisfies the cron expression. Note that
         * milliseconds are ignored, so two Dates falling on different milliseconds
         * of the same second will always have the same result here.
         *
         * @param date the date to evaluate
         * @return a boolean indicating whether the given date satisfies the cron
         *         expression
         */
        public boolean isSatisfiedBy(Date date) {
            Calendar testDateCal = Calendar.getInstance();
            testDateCal.setTime(date);
            testDateCal.set(Calendar.MILLISECOND, 0);
            Date originalDate = testDateCal.getTime();

            testDateCal.add(Calendar.SECOND, -1);

            Date timeAfter = getTimeAfter(testDateCal.getTime());

            return ((timeAfter != null) && (timeAfter.equals(originalDate)));
        }

        /**
         * Returns the next date/time <I>after</I> the given date/time which
         * satisfies the cron expression.
         *
         * @param date the date/time at which to begin the search for the next valid
         *             date/time
         * @return the next valid date/time
         */
        public Date getNextValidTimeAfter(Date date) {
            return getTimeAfter(date);
        }

        /**
         * Returns the next date/time <I>after</I> the given date/time which does
         * <I>not</I> satisfy the expression
         *
         * @param date the date/time at which to begin the search for the next
         *             invalid date/time
         * @return the next valid date/time
         */
        public Date getNextInvalidTimeAfter(Date date) {
            long difference = 1000;

            //move back to the nearest second so differences will be accurate
            Calendar adjustCal = Calendar.getInstance();
            adjustCal.setTime(date);
            adjustCal.set(Calendar.MILLISECOND, 0);
            Date lastDate = adjustCal.getTime();

            Date newDate = null;

            //keep getting the next included time until it's farther than one second
            // apart. At that point, lastDate is the last valid fire time. We return
            // the second immediately following it.
            while (difference == 1000) {
                newDate = getTimeAfter(lastDate);

                difference = newDate.getTime() - lastDate.getTime();

                if (difference == 1000) {
                    lastDate = newDate;
                }
            }

            return new Date(lastDate.getTime() + 1000);
        }

        /**
         * Return the interval between the next valid date and the one after
         *
         * @param date the date/time at which to begin the search
         * @return the number of milliseconds between the next valid and the one after
         */
        public long getNextInterval(Date date) {
            Date nextValid = getNextValidTimeAfter(date);
            Date nextInvalid = getNextInvalidTimeAfter(nextValid);
            Date nextNextValid = getNextValidTimeAfter(nextInvalid);
            return nextNextValid.getTime() - nextValid.getTime();
        }

        /**
         * Returns the time zone for which this <code>CronExpression</code>
         * will be resolved.
         */
        public TimeZone getTimeZone() {
            if (timeZone == null) {
                timeZone = TimeZone.getDefault();
            }

            return timeZone;
        }

        /**
         * Sets the time zone for which  this <code>CronExpression</code>
         * will be resolved.
         */
        public void setTimeZone(TimeZone timeZone) {
            this.timeZone = timeZone;
        }

        /**
         * Returns the string representation of the <CODE>CronExpression</CODE>
         *
         * @return a string representation of the <CODE>CronExpression</CODE>
         */
        @Override
        public String toString() {
            return cronExpression;
        }

        /**
         * Indicates whether the specified cron expression can be parsed into a
         * valid cron expression
         *
         * @param cronExpression the expression to evaluate
         * @return a boolean indicating whether the given expression is a valid cron
         *         expression
         */
        public static boolean isValidExpression(String cronExpression) {

            try {
                new CronExpression(cronExpression);
            } catch (ParseException pe) {
                return false;
            }

            return true;
        }

        ////////////////////////////////////////////////////////////////////////////
        //
        // Expression Parsing Functions
        //
        ////////////////////////////////////////////////////////////////////////////
        protected void buildExpression(String expression) throws ParseException {
            expressionParsed = true;

            try {

                if (seconds == null) {
                    seconds = new TreeSet<Integer>();
                }
                if (minutes == null) {
                    minutes = new TreeSet<Integer>();
                }
                if (hours == null) {
                    hours = new TreeSet<Integer>();
                }
                if (daysOfMonth == null) {
                    daysOfMonth = new TreeSet<Integer>();
                }
                if (months == null) {
                    months = new TreeSet<Integer>();
                }
                if (daysOfWeek == null) {
                    daysOfWeek = new TreeSet<Integer>();
                }
                if (years == null) {
                    years = new TreeSet<Integer>();
                }

                int exprOn = SECOND;

                StringTokenizer exprsTok = new StringTokenizer(expression, " \t",
                        false);

                while (exprsTok.hasMoreTokens() && exprOn <= YEAR) {
                    String expr = exprsTok.nextToken().trim();
                    StringTokenizer vTok = new StringTokenizer(expr, ",");
                    while (vTok.hasMoreTokens()) {
                        String v = vTok.nextToken();
                        storeExpressionVals(0, v, exprOn);
                    }

                    exprOn++;
                }

                if (exprOn <= DAY_OF_WEEK) {
                    throw new ParseException("Unexpected end of expression.",
                            expression.length());
                }

                if (exprOn <= YEAR) {
                    storeExpressionVals(0, "*", YEAR);
                }

            } catch (ParseException pe) {
                throw pe;
            } catch (Exception e) {
                throw new ParseException("Illegal cron expression format (" + e.toString() + ")", 0);
            }
        }

        protected int storeExpressionVals(int pos, String s, int type)
                throws ParseException {

            int incr = 0;
            int i = skipWhiteSpace(pos, s);
            if (i >= s.length()) {
                return i;
            }
            char c = s.charAt(i);
            if ((c >= 'A') && (c <= 'Z') && (!s.equals("L")) && (!s.equals("LW"))) {
                String sub = s.substring(i, i + 3);
                int sval = -1;
                int eval = -1;
                if (type == MONTH) {
                    sval = getMonthNumber(sub) + 1;
                    if (sval < 0) {
                        throw new ParseException("Invalid Month value: '" + sub + "'", i);
                    }
                    if (s.length() > i + 3) {
                        c = s.charAt(i + 3);
                        if (c == '-') {
                            i += 4;
                            sub = s.substring(i, i + 3);
                            eval = getMonthNumber(sub) + 1;
                            if (eval < 0) {
                                throw new ParseException("Invalid Month value: '" + sub + "'", i);
                            }
                        }
                    }
                } else if (type == DAY_OF_WEEK) {
                    sval = getDayOfWeekNumber(sub);
                    if (sval < 0) {
                        throw new ParseException("Invalid Day-of-Week value: '" + sub + "'", i);
                    }
                    if (s.length() > i + 3) {
                        c = s.charAt(i + 3);
                        if (c == '-') {
                            i += 4;
                            sub = s.substring(i, i + 3);
                            eval = getDayOfWeekNumber(sub);
                            if (eval < 0) {
                                throw new ParseException(
                                        "Invalid Day-of-Week value: '" + sub + "'", i);
                            }
                            if (sval > eval) {
                                throw new ParseException(
                                        "Invalid Day-of-Week sequence: " + sval + " > " + eval, i);
                            }
                        } else if (c == '#') {
                            try {
                                i += 4;
                                nthdayOfWeek = Integer.parseInt(s.substring(i));
                                if (nthdayOfWeek < 1 || nthdayOfWeek > 5) {
                                    throw new Exception();
                                }
                            } catch (Exception e) {
                                throw new ParseException(
                                        "A numeric value between 1 and 5 must follow the '#' option",
                                        i);
                            }
                        } else if (c == 'L') {
                            lastdayOfWeek = true;
                            i++;
                        }
                    }

                } else {
                    throw new ParseException(
                            "Illegal characters for this position: '" + sub + "'",
                            i);
                }
                if (eval != -1) {
                    incr = 1;
                }
                addToSet(sval, eval, incr, type);
                return (i + 3);
            }

            if (c == '?') {
                i++;
                if ((i + 1) < s.length() && (s.charAt(i) != ' ' && s.charAt(i + 1) != '\t')) {
                    throw new ParseException("Illegal character after '?': " + s.charAt(i), i);
                }
                if (type != DAY_OF_WEEK && type != DAY_OF_MONTH) {
                    throw new ParseException(
                            "'?' can only be specfied for Day-of-Month or Day-of-Week.",
                            i);
                }
                if (type == DAY_OF_WEEK && !lastdayOfMonth) {
                    int val = daysOfMonth.last().intValue();
                    if (val == NO_SPEC_INT) {
                        throw new ParseException(
                                "'?' can only be specfied for Day-of-Month -OR- Day-of-Week.",
                                i);
                    }
                }

                addToSet(NO_SPEC_INT, -1, 0, type);
                return i;
            }

            if (c == '*' || c == '/') {
                if (c == '*' && (i + 1) >= s.length()) {
                    addToSet(ALL_SPEC_INT, -1, incr, type);
                    return i + 1;
                } else if (c == '/' && ((i + 1) >= s.length() || s.charAt(i + 1) == ' ' || s.charAt(i + 1) == '\t')) {
                    throw new ParseException("'/' must be followed by an integer.", i);
                } else if (c == '*') {
                    i++;
                }
                c = s.charAt(i);
                if (c == '/') { // is an increment specified?
                    i++;
                    if (i >= s.length()) {
                        throw new ParseException("Unexpected end of string.", i);
                    }

                    incr = getNumericValue(s, i);

                    i++;
                    if (incr > 10) {
                        i++;
                    }
                    if (incr > 59 && (type == SECOND || type == MINUTE)) {
                        throw new ParseException("Increment > 60 : " + incr, i);
                    } else if (incr > 23 && (type == HOUR)) {
                        throw new ParseException("Increment > 24 : " + incr, i);
                    } else if (incr > 31 && (type == DAY_OF_MONTH)) {
                        throw new ParseException("Increment > 31 : " + incr, i);
                    } else if (incr > 7 && (type == DAY_OF_WEEK)) {
                        throw new ParseException("Increment > 7 : " + incr, i);
                    } else if (incr > 12 && (type == MONTH)) {
                        throw new ParseException("Increment > 12 : " + incr, i);
                    }
                } else {
                    incr = 1;
                }

                addToSet(ALL_SPEC_INT, -1, incr, type);
                return i;
            } else if (c == 'L') {
                i++;
                if (type == DAY_OF_MONTH) {
                    lastdayOfMonth = true;
                }
                if (type == DAY_OF_WEEK) {
                    addToSet(7, 7, 0, type);
                }
                if (type == DAY_OF_MONTH && s.length() > i) {
                    c = s.charAt(i);
                    if (c == 'W') {
                        nearestWeekday = true;
                        i++;
                    }
                }
                return i;
            } else if (c >= '0' && c <= '9') {
                int val = Integer.parseInt(String.valueOf(c));
                i++;
                if (i >= s.length()) {
                    addToSet(val, -1, -1, type);
                } else {
                    c = s.charAt(i);
                    if (c >= '0' && c <= '9') {
                        ValueSet vs = getValue(val, s, i);
                        val = vs.value;
                        i = vs.pos;
                    }
                    i = checkNext(i, s, val, type);
                    return i;
                }
            } else {
                throw new ParseException("Unexpected character: " + c, i);
            }

            return i;
        }

        protected int checkNext(int pos, String s, int val, int type)
                throws ParseException {

            int end = -1;
            int i = pos;

            if (i >= s.length()) {
                addToSet(val, end, -1, type);
                return i;
            }

            char c = s.charAt(pos);

            if (c == 'L') {
                if (type == DAY_OF_WEEK) {
                    lastdayOfWeek = true;
                } else {
                    throw new ParseException("'L' option is not valid here. (pos=" + i + ")", i);
                }
                TreeSet<Integer> set = getSet(type);
                set.add(new Integer(val));
                i++;
                return i;
            }

            if (c == 'W') {
                if (type == DAY_OF_MONTH) {
                    nearestWeekday = true;
                } else {
                    throw new ParseException("'W' option is not valid here. (pos=" + i + ")", i);
                }
                TreeSet<Integer> set = getSet(type);
                set.add(new Integer(val));
                i++;
                return i;
            }

            if (c == '#') {
                if (type != DAY_OF_WEEK) {
                    throw new ParseException("'#' option is not valid here. (pos=" + i + ")", i);
                }
                i++;
                try {
                    nthdayOfWeek = Integer.parseInt(s.substring(i));
                    if (nthdayOfWeek < 1 || nthdayOfWeek > 5) {
                        throw new Exception();
                    }
                } catch (Exception e) {
                    throw new ParseException(
                            "A numeric value between 1 and 5 must follow the '#' option",
                            i);
                }

                TreeSet<Integer> set = getSet(type);
                set.add(new Integer(val));
                i++;
                return i;
            }

            if (c == '-') {
                i++;
                c = s.charAt(i);
                int v = Integer.parseInt(String.valueOf(c));
                end = v;
                i++;
                if (i >= s.length()) {
                    addToSet(val, end, 1, type);
                    return i;
                }
                c = s.charAt(i);
                if (c >= '0' && c <= '9') {
                    ValueSet vs = getValue(v, s, i);
                    int v1 = vs.value;
                    end = v1;
                    i = vs.pos;
                }
                if (i < s.length() && ((c = s.charAt(i)) == '/')) {
                    i++;
                    c = s.charAt(i);
                    int v2 = Integer.parseInt(String.valueOf(c));
                    i++;
                    if (i >= s.length()) {
                        addToSet(val, end, v2, type);
                        return i;
                    }
                    c = s.charAt(i);
                    if (c >= '0' && c <= '9') {
                        ValueSet vs = getValue(v2, s, i);
                        int v3 = vs.value;
                        addToSet(val, end, v3, type);
                        i = vs.pos;
                        return i;
                    } else {
                        addToSet(val, end, v2, type);
                        return i;
                    }
                } else {
                    addToSet(val, end, 1, type);
                    return i;
                }
            }

            if (c == '/') {
                i++;
                c = s.charAt(i);
                int v2 = Integer.parseInt(String.valueOf(c));
                i++;
                if (i >= s.length()) {
                    addToSet(val, end, v2, type);
                    return i;
                }
                c = s.charAt(i);
                if (c >= '0' && c <= '9') {
                    ValueSet vs = getValue(v2, s, i);
                    int v3 = vs.value;
                    addToSet(val, end, v3, type);
                    i = vs.pos;
                    return i;
                } else {
                    throw new ParseException("Unexpected character '" + c + "' after '/'", i);
                }
            }

            addToSet(val, end, 0, type);
            i++;
            return i;
        }

        public String getCronExpression() {
            return cronExpression;
        }

        public String getExpressionSummary() {
            StringBuffer buf = new StringBuffer();

            buf.append("seconds: ");
            buf.append(getExpressionSetSummary(seconds));
            buf.append("\n");
            buf.append("minutes: ");
            buf.append(getExpressionSetSummary(minutes));
            buf.append("\n");
            buf.append("hours: ");
            buf.append(getExpressionSetSummary(hours));
            buf.append("\n");
            buf.append("daysOfMonth: ");
            buf.append(getExpressionSetSummary(daysOfMonth));
            buf.append("\n");
            buf.append("months: ");
            buf.append(getExpressionSetSummary(months));
            buf.append("\n");
            buf.append("daysOfWeek: ");
            buf.append(getExpressionSetSummary(daysOfWeek));
            buf.append("\n");
            buf.append("lastdayOfWeek: ");
            buf.append(lastdayOfWeek);
            buf.append("\n");
            buf.append("nearestWeekday: ");
            buf.append(nearestWeekday);
            buf.append("\n");
            buf.append("NthDayOfWeek: ");
            buf.append(nthdayOfWeek);
            buf.append("\n");
            buf.append("lastdayOfMonth: ");
            buf.append(lastdayOfMonth);
            buf.append("\n");
            buf.append("years: ");
            buf.append(getExpressionSetSummary(years));
            buf.append("\n");

            return buf.toString();
        }

        protected String getExpressionSetSummary(java.util.Set<Integer> set) {

            if (set.contains(NO_SPEC)) {
                return "?";
            }
            if (set.contains(ALL_SPEC)) {
                return "*";
            }

            StringBuffer buf = new StringBuffer();

            Iterator<Integer> itr = set.iterator();
            boolean first = true;
            while (itr.hasNext()) {
                Integer iVal = itr.next();
                String val = iVal.toString();
                if (!first) {
                    buf.append(",");
                }
                buf.append(val);
                first = false;
            }

            return buf.toString();
        }

        protected String getExpressionSetSummary(java.util.ArrayList<Integer> list) {

            if (list.contains(NO_SPEC)) {
                return "?";
            }
            if (list.contains(ALL_SPEC)) {
                return "*";
            }

            StringBuffer buf = new StringBuffer();

            Iterator<Integer> itr = list.iterator();
            boolean first = true;
            while (itr.hasNext()) {
                Integer iVal = itr.next();
                String val = iVal.toString();
                if (!first) {
                    buf.append(",");
                }
                buf.append(val);
                first = false;
            }

            return buf.toString();
        }

        protected int skipWhiteSpace(int i, String s) {
            for (; i < s.length() && (s.charAt(i) == ' ' || s.charAt(i) == '\t'); i++) {
            }

            return i;
        }

        protected int findNextWhiteSpace(int i, String s) {
            for (; i < s.length() && (s.charAt(i) != ' ' || s.charAt(i) != '\t'); i++) {
            }

            return i;
        }

        protected void addToSet(int val, int end, int incr, int type)
                throws ParseException {

            TreeSet<Integer> set = getSet(type);

            if (type == SECOND || type == MINUTE) {
                if ((val < 0 || val > 59 || end > 59) && (val != ALL_SPEC_INT)) {
                    throw new ParseException(
                            "Minute and Second values must be between 0 and 59",
                            -1);
                }
            } else if (type == HOUR) {
                if ((val < 0 || val > 23 || end > 23) && (val != ALL_SPEC_INT)) {
                    throw new ParseException(
                            "Hour values must be between 0 and 23", -1);
                }
            } else if (type == DAY_OF_MONTH) {
                if ((val < 1 || val > 31 || end > 31) && (val != ALL_SPEC_INT) && (val != NO_SPEC_INT)) {
                    throw new ParseException(
                            "Day of month values must be between 1 and 31", -1);
                }
            } else if (type == MONTH) {
                if ((val < 1 || val > 12 || end > 12) && (val != ALL_SPEC_INT)) {
                    throw new ParseException(
                            "Month values must be between 1 and 12", -1);
                }
            } else if (type == DAY_OF_WEEK) {
                if ((val == 0 || val > 7 || end > 7) && (val != ALL_SPEC_INT) && (val != NO_SPEC_INT)) {
                    throw new ParseException(
                            "Day-of-Week values must be between 1 and 7", -1);
                }
            }

            if ((incr == 0 || incr == -1) && val != ALL_SPEC_INT) {
                if (val != -1) {
                    set.add(new Integer(val));
                } else {
                    set.add(NO_SPEC);
                }

                return;
            }

            int startAt = val;
            int stopAt = end;

            if (val == ALL_SPEC_INT && incr <= 0) {
                incr = 1;
                set.add(ALL_SPEC); // put in a marker, but also fill values
            }

            if (type == SECOND || type == MINUTE) {
                if (stopAt == -1) {
                    stopAt = 59;
                }
                if (startAt == -1 || startAt == ALL_SPEC_INT) {
                    startAt = 0;
                }
            } else if (type == HOUR) {
                if (stopAt == -1) {
                    stopAt = 23;
                }
                if (startAt == -1 || startAt == ALL_SPEC_INT) {
                    startAt = 0;
                }
            } else if (type == DAY_OF_MONTH) {
                if (stopAt == -1) {
                    stopAt = 31;
                }
                if (startAt == -1 || startAt == ALL_SPEC_INT) {
                    startAt = 1;
                }
            } else if (type == MONTH) {
                if (stopAt == -1) {
                    stopAt = 12;
                }
                if (startAt == -1 || startAt == ALL_SPEC_INT) {
                    startAt = 1;
                }
            } else if (type == DAY_OF_WEEK) {
                if (stopAt == -1) {
                    stopAt = 7;
                }
                if (startAt == -1 || startAt == ALL_SPEC_INT) {
                    startAt = 1;
                }
            } else if (type == YEAR) {
                if (stopAt == -1) {
                    stopAt = 2099;
                }
                if (startAt == -1 || startAt == ALL_SPEC_INT) {
                    startAt = 1970;
                }
            }

            for (int i = startAt; i <= stopAt; i += incr) {
                set.add(new Integer(i));
            }
        }

        protected TreeSet<Integer> getSet(int type) {
            switch (type) {
                case SECOND:
                    return seconds;
                case MINUTE:
                    return minutes;
                case HOUR:
                    return hours;
                case DAY_OF_MONTH:
                    return daysOfMonth;
                case MONTH:
                    return months;
                case DAY_OF_WEEK:
                    return daysOfWeek;
                case YEAR:
                    return years;
                default:
                    return null;
            }
        }

        protected ValueSet getValue(int v, String s, int i) {
            char c = s.charAt(i);
            String s1 = String.valueOf(v);
            while (c >= '0' && c <= '9') {
                s1 += c;
                i++;
                if (i >= s.length()) {
                    break;
                }
                c = s.charAt(i);
            }
            ValueSet val = new ValueSet();

            val.pos = (i < s.length()) ? i : i + 1;
            val.value = Integer.parseInt(s1);
            return val;
        }

        protected int getNumericValue(String s, int i) {
            int endOfVal = findNextWhiteSpace(i, s);
            String val = s.substring(i, endOfVal);
            return Integer.parseInt(val);
        }

        protected int getMonthNumber(String s) {
            Integer integer = monthMap.get(s);

            if (integer == null) {
                return -1;
            }

            return integer.intValue();
        }

        protected int getDayOfWeekNumber(String s) {
            Integer integer = dayMap.get(s);

            if (integer == null) {
                return -1;
            }

            return integer.intValue();
        }

        ////////////////////////////////////////////////////////////////////////////
        //
        // Computation Functions
        //
        ////////////////////////////////////////////////////////////////////////////
        protected Date getTimeAfter(Date afterTime) {

            Calendar cl = Calendar.getInstance(getTimeZone());

            // move ahead one second, since we're computing the time *after* the
            // given time
            afterTime = new Date(afterTime.getTime() + 1000);
            // CronTrigger does not deal with milliseconds
            cl.setTime(afterTime);
            cl.set(Calendar.MILLISECOND, 0);

            boolean gotOne = false;
            // loop until we've computed the next time, or we've past the endTime
            while (!gotOne) {

                //if (endTime != null && cl.getTime().after(endTime)) return null;

                SortedSet<Integer> st = null;
                int t = 0;

                int sec = cl.get(Calendar.SECOND);
                int min = cl.get(Calendar.MINUTE);

                // get second.................................................
                st = seconds.tailSet(new Integer(sec));
                if (st != null && st.size() != 0) {
                    sec = st.first().intValue();
                } else {
                    sec = seconds.first().intValue();
                    min++;
                    cl.set(Calendar.MINUTE, min);
                }
                cl.set(Calendar.SECOND, sec);

                min = cl.get(Calendar.MINUTE);
                int hr = cl.get(Calendar.HOUR_OF_DAY);
                t = -1;

                // get minute.................................................
                st = minutes.tailSet(new Integer(min));
                if (st != null && st.size() != 0) {
                    t = min;
                    min = st.first().intValue();
                } else {
                    min = minutes.first().intValue();
                    hr++;
                }
                if (min != t) {
                    cl.set(Calendar.SECOND, 0);
                    cl.set(Calendar.MINUTE, min);
                    setCalendarHour(cl, hr);
                    continue;
                }
                cl.set(Calendar.MINUTE, min);

                hr = cl.get(Calendar.HOUR_OF_DAY);
                int day = cl.get(Calendar.DAY_OF_MONTH);
                t = -1;

                // get hour...................................................
                st = hours.tailSet(new Integer(hr));
                if (st != null && st.size() != 0) {
                    t = hr;
                    hr = st.first().intValue();
                } else {
                    hr = hours.first().intValue();
                    day++;
                }
                if (hr != t) {
                    cl.set(Calendar.SECOND, 0);
                    cl.set(Calendar.MINUTE, 0);
                    cl.set(Calendar.DAY_OF_MONTH, day);
                    setCalendarHour(cl, hr);
                    continue;
                }
                cl.set(Calendar.HOUR_OF_DAY, hr);

                day = cl.get(Calendar.DAY_OF_MONTH);
                int mon = cl.get(Calendar.MONTH) + 1;
                // '+ 1' because calendar is 0-based for this field, and we are
                // 1-based
                t = -1;
                int tmon = mon;

                // get day...................................................
                boolean dayOfMSpec = !daysOfMonth.contains(NO_SPEC);
                boolean dayOfWSpec = !daysOfWeek.contains(NO_SPEC);
                if (dayOfMSpec && !dayOfWSpec) { // get day by day of month rule
                    st = daysOfMonth.tailSet(new Integer(day));
                    if (lastdayOfMonth) {
                        if (!nearestWeekday) {
                            t = day;
                            day = getLastDayOfMonth(mon, cl.get(Calendar.YEAR));
                        } else {
                            t = day;
                            day = getLastDayOfMonth(mon, cl.get(Calendar.YEAR));

                            java.util.Calendar tcal = java.util.Calendar.getInstance();
                            tcal.set(Calendar.SECOND, 0);
                            tcal.set(Calendar.MINUTE, 0);
                            tcal.set(Calendar.HOUR_OF_DAY, 0);
                            tcal.set(Calendar.DAY_OF_MONTH, day);
                            tcal.set(Calendar.MONTH, mon - 1);
                            tcal.set(Calendar.YEAR, cl.get(Calendar.YEAR));

                            int ldom = getLastDayOfMonth(mon, cl.get(Calendar.YEAR));
                            int dow = tcal.get(Calendar.DAY_OF_WEEK);

                            if (dow == Calendar.SATURDAY && day == 1) {
                                day += 2;
                            } else if (dow == Calendar.SATURDAY) {
                                day -= 1;
                            } else if (dow == Calendar.SUNDAY && day == ldom) {
                                day -= 2;
                            } else if (dow == Calendar.SUNDAY) {
                                day += 1;
                            }

                            tcal.set(Calendar.SECOND, sec);
                            tcal.set(Calendar.MINUTE, min);
                            tcal.set(Calendar.HOUR_OF_DAY, hr);
                            tcal.set(Calendar.DAY_OF_MONTH, day);
                            tcal.set(Calendar.MONTH, mon - 1);
                            Date nTime = tcal.getTime();
                            if (nTime.before(afterTime)) {
                                day = 1;
                                mon++;
                            }
                        }
                    } else if (nearestWeekday) {
                        t = day;
                        day = daysOfMonth.first().intValue();

                        java.util.Calendar tcal = java.util.Calendar.getInstance();
                        tcal.set(Calendar.SECOND, 0);
                        tcal.set(Calendar.MINUTE, 0);
                        tcal.set(Calendar.HOUR_OF_DAY, 0);
                        tcal.set(Calendar.DAY_OF_MONTH, day);
                        tcal.set(Calendar.MONTH, mon - 1);
                        tcal.set(Calendar.YEAR, cl.get(Calendar.YEAR));

                        int ldom = getLastDayOfMonth(mon, cl.get(Calendar.YEAR));
                        int dow = tcal.get(Calendar.DAY_OF_WEEK);

                        if (dow == Calendar.SATURDAY && day == 1) {
                            day += 2;
                        } else if (dow == Calendar.SATURDAY) {
                            day -= 1;
                        } else if (dow == Calendar.SUNDAY && day == ldom) {
                            day -= 2;
                        } else if (dow == Calendar.SUNDAY) {
                            day += 1;
                        }


                        tcal.set(Calendar.SECOND, sec);
                        tcal.set(Calendar.MINUTE, min);
                        tcal.set(Calendar.HOUR_OF_DAY, hr);
                        tcal.set(Calendar.DAY_OF_MONTH, day);
                        tcal.set(Calendar.MONTH, mon - 1);
                        Date nTime = tcal.getTime();
                        if (nTime.before(afterTime)) {
                            day = daysOfMonth.first().intValue();
                            mon++;
                        }
                    } else if (st != null && st.size() != 0) {
                        t = day;
                        day = st.first().intValue();
                    } else {
                        day = daysOfMonth.first().intValue();
                        mon++;
                    }

                    if (day != t || mon != tmon) {
                        cl.set(Calendar.SECOND, 0);
                        cl.set(Calendar.MINUTE, 0);
                        cl.set(Calendar.HOUR_OF_DAY, 0);
                        cl.set(Calendar.DAY_OF_MONTH, day);
                        cl.set(Calendar.MONTH, mon - 1);
                        // '- 1' because calendar is 0-based for this field, and we
                        // are 1-based
                        continue;
                    }
                } else if (dayOfWSpec && !dayOfMSpec) { // get day by day of week rule
                    if (lastdayOfWeek) {
                        // are we looking for the last day of the month?
                        int dow = daysOfWeek.first().intValue(); // desired
                        // d-o-w
                        int cDow = cl.get(Calendar.DAY_OF_WEEK); // current d-o-w
                        int daysToAdd = 0;
                        if (cDow < dow) {
                            daysToAdd = dow - cDow;
                        }
                        if (cDow > dow) {
                            daysToAdd = dow + (7 - cDow);
                        }

                        int lDay = getLastDayOfMonth(mon, cl.get(Calendar.YEAR));

                        if (day + daysToAdd > lDay) { // did we already miss the
                            // last one?
                            cl.set(Calendar.SECOND, 0);
                            cl.set(Calendar.MINUTE, 0);
                            cl.set(Calendar.HOUR_OF_DAY, 0);
                            cl.set(Calendar.DAY_OF_MONTH, 1);
                            cl.set(Calendar.MONTH, mon);
                            // no '- 1' here because we are promoting the month
                            continue;
                        }

                        // find date of last occurance of this day in this month...
                        while ((day + daysToAdd + 7) <= lDay) {
                            daysToAdd += 7;
                        }

                        day += daysToAdd;

                        if (daysToAdd > 0) {
                            cl.set(Calendar.SECOND, 0);
                            cl.set(Calendar.MINUTE, 0);
                            cl.set(Calendar.HOUR_OF_DAY, 0);
                            cl.set(Calendar.DAY_OF_MONTH, day);
                            cl.set(Calendar.MONTH, mon - 1);
                            // '- 1' here because we are not promoting the month
                            continue;
                        }

                    } else if (nthdayOfWeek != 0) {
                        // are we looking for the Nth day in the month?
                        int dow = daysOfWeek.first().intValue(); // desired
                        // d-o-w
                        int cDow = cl.get(Calendar.DAY_OF_WEEK); // current d-o-w
                        int daysToAdd = 0;
                        if (cDow < dow) {
                            daysToAdd = dow - cDow;
                        } else if (cDow > dow) {
                            daysToAdd = dow + (7 - cDow);
                        }

                        boolean dayShifted = false;
                        if (daysToAdd > 0) {
                            dayShifted = true;
                        }

                        day += daysToAdd;
                        int weekOfMonth = day / 7;
                        if (day % 7 > 0) {
                            weekOfMonth++;
                        }

                        daysToAdd = (nthdayOfWeek - weekOfMonth) * 7;
                        day += daysToAdd;
                        if (daysToAdd < 0 || day > getLastDayOfMonth(mon, cl.get(Calendar.YEAR))) {
                            cl.set(Calendar.SECOND, 0);
                            cl.set(Calendar.MINUTE, 0);
                            cl.set(Calendar.HOUR_OF_DAY, 0);
                            cl.set(Calendar.DAY_OF_MONTH, 1);
                            cl.set(Calendar.MONTH, mon);
                            // no '- 1' here because we are promoting the month
                            continue;
                        } else if (daysToAdd > 0 || dayShifted) {
                            cl.set(Calendar.SECOND, 0);
                            cl.set(Calendar.MINUTE, 0);
                            cl.set(Calendar.HOUR_OF_DAY, 0);
                            cl.set(Calendar.DAY_OF_MONTH, day);
                            cl.set(Calendar.MONTH, mon - 1);
                            // '- 1' here because we are NOT promoting the month
                            continue;
                        }
                    } else {
                        int cDow = cl.get(Calendar.DAY_OF_WEEK); // current d-o-w
                        int dow = daysOfWeek.first().intValue(); // desired
                        // d-o-w
                        st = daysOfWeek.tailSet(new Integer(cDow));
                        if (st != null && st.size() > 0) {
                            dow = st.first().intValue();
                        }

                        int daysToAdd = 0;
                        if (cDow < dow) {
                            daysToAdd = dow - cDow;
                        }
                        if (cDow > dow) {
                            daysToAdd = dow + (7 - cDow);
                        }

                        int lDay = getLastDayOfMonth(mon, cl.get(Calendar.YEAR));

                        if (day + daysToAdd > lDay) { // will we pass the end of
                            // the month?
                            cl.set(Calendar.SECOND, 0);
                            cl.set(Calendar.MINUTE, 0);
                            cl.set(Calendar.HOUR_OF_DAY, 0);
                            cl.set(Calendar.DAY_OF_MONTH, 1);
                            cl.set(Calendar.MONTH, mon);
                            // no '- 1' here because we are promoting the month
                            continue;
                        } else if (daysToAdd > 0) { // are we swithing days?
                            cl.set(Calendar.SECOND, 0);
                            cl.set(Calendar.MINUTE, 0);
                            cl.set(Calendar.HOUR_OF_DAY, 0);
                            cl.set(Calendar.DAY_OF_MONTH, day + daysToAdd);
                            cl.set(Calendar.MONTH, mon - 1);
                            // '- 1' because calendar is 0-based for this field,
                            // and we are 1-based
                            continue;
                        }
                    }
                } else { // dayOfWSpec && !dayOfMSpec
                    throw new UnsupportedOperationException(
                            "Support for specifying both a day-of-week AND a day-of-month parameter is not implemented.");
                }
                cl.set(Calendar.DAY_OF_MONTH, day);

                mon = cl.get(Calendar.MONTH) + 1;
                // '+ 1' because calendar is 0-based for this field, and we are
                // 1-based
                int year = cl.get(Calendar.YEAR);
                t = -1;

                // test for expressions that never generate a valid fire date,
                // but keep looping...
                if (year > 2099) {
                    return null;
                }

                // get month...................................................
                st = months.tailSet(new Integer(mon));
                if (st != null && st.size() != 0) {
                    t = mon;
                    mon = st.first().intValue();
                } else {
                    mon = months.first().intValue();
                    year++;
                }
                if (mon != t) {
                    cl.set(Calendar.SECOND, 0);
                    cl.set(Calendar.MINUTE, 0);
                    cl.set(Calendar.HOUR_OF_DAY, 0);
                    cl.set(Calendar.DAY_OF_MONTH, 1);
                    cl.set(Calendar.MONTH, mon - 1);
                    // '- 1' because calendar is 0-based for this field, and we are
                    // 1-based
                    cl.set(Calendar.YEAR, year);
                    continue;
                }
                cl.set(Calendar.MONTH, mon - 1);
                // '- 1' because calendar is 0-based for this field, and we are
                // 1-based

                year = cl.get(Calendar.YEAR);
                t = -1;

                // get year...................................................
                st = years.tailSet(new Integer(year));
                if (st != null && st.size() != 0) {
                    t = year;
                    year = st.first().intValue();
                } else {
                    return null; // ran out of years...
                }

                if (year != t) {
                    cl.set(Calendar.SECOND, 0);
                    cl.set(Calendar.MINUTE, 0);
                    cl.set(Calendar.HOUR_OF_DAY, 0);
                    cl.set(Calendar.DAY_OF_MONTH, 1);
                    cl.set(Calendar.MONTH, 0);
                    // '- 1' because calendar is 0-based for this field, and we are
                    // 1-based
                    cl.set(Calendar.YEAR, year);
                    continue;
                }
                cl.set(Calendar.YEAR, year);

                gotOne = true;
            } // while( !done )

            return cl.getTime();
        }

        /**
         * Advance the calendar to the particular hour paying particular attention
         * to daylight saving problems.
         *
         * @param cal
         * @param hour
         */
        protected void setCalendarHour(Calendar cal, int hour) {
            cal.set(java.util.Calendar.HOUR_OF_DAY, hour);
            if (cal.get(java.util.Calendar.HOUR_OF_DAY) != hour && hour != 24) {
                cal.set(java.util.Calendar.HOUR_OF_DAY, hour + 1);
            }
        }

        /**
         * NOT YET IMPLEMENTED: Returns the time before the given time
         * that the <code>CronExpression</code> matches.
         */
        protected Date getTimeBefore(Date endTime) {
            throw new UnsupportedOperationException("not implemented");
        }

        /**
         * NOT YET IMPLEMENTED: Returns the final time that the
         * <code>CronExpression</code> will match.
         */
        public Date getFinalFireTime() {
            throw new UnsupportedOperationException("not implemented");
        }

        protected boolean isLeapYear(int year) {
            return ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0));
        }

        protected int getLastDayOfMonth(int monthNum, int year) {

            switch (monthNum) {
                case 1:
                    return 31;
                case 2:
                    return (isLeapYear(year)) ? 29 : 28;
                case 3:
                    return 31;
                case 4:
                    return 30;
                case 5:
                    return 31;
                case 6:
                    return 30;
                case 7:
                    return 31;
                case 8:
                    return 31;
                case 9:
                    return 30;
                case 10:
                    return 31;
                case 11:
                    return 30;
                case 12:
                    return 31;
                default:
                    throw new IllegalArgumentException("Illegal month number: " + monthNum);
            }
        }

        private void readObject(java.io.ObjectInputStream stream)
                throws java.io.IOException, ClassNotFoundException {

            stream.defaultReadObject();
            try {
                buildExpression(cronExpression);
            } catch (Exception ignore) {
            } // never happens
        }

        @Override
        public Object clone() {
            CronExpression copy = null;
            try {
                copy = new CronExpression(getCronExpression());
                copy.setTimeZone(getTimeZone());
            } catch (ParseException ex) { // never happens since the source is valid...
                throw new IncompatibleClassChangeError("Not Cloneable.");
            }
            return copy;
        }
    }

    private static class ValueSet {

        public int value;
        public int pos;
    }
}
